Manufacture of ammonium sulphate



Patented Oct. 31, 1939 UNITED STATES PATENT OFFICE John Wilfred Richard Rayner, Norton-on-Tees,

England, assignor to Imperial Chemical Industries Limited, Britain Nd Drawing.

a corporation of Great Application November 5, 1937,

Serial No. 172,924. In Great Britain November 11, 1936 2 Claims.

This invention relates to the manufacture of ammonium sulphate, and more particularly to a method of controlling the size and form of ammonium sulphate crystals during manufacture.

5 The invention is applicable to the formation of crystals by the evaporation of ammonium sulphate solutions or by crystallisation from solutions which are maintained substantially supersaturated, e. g. such as are obtained in the so-called saturator process, where ammonia and sulphuric acid are allowed to react in a liquor already saturated with ammonium sulphate.

It is known that the form and size of ammonium sulphate crystals are influenced by the presence of trivalent iron aluminium or chromium ions in the mother liquor, and that the form and size of the crystals can be controlled by legulating the concentrations of these ions in the mother liquor, due regard being paid to other factors bearing on the crystal shape and 20 form, e. g. the acidity of the liquor. In general it is desirable to keep the concentration of the said ions within certain limits.

Thus if the concentration of the trivalent ions of iron, aluminium or chromium in the mother liquor is allowed to reach an excessive value the crystals are obtained in the form of fine needles which readily break down to dust when dried. For many purposes, however, it is desirable to produce crystals free from dust, and in a form and size such that they do not crumble or cake in transit or storage. These properties are particularly desirable when the ammonium sulphate is to be used as a fertilizer, regularity in crystal size allowing even distribution over the land to be treated.

While the size and form of the ammonium sulphate crystals may be controlled by the presence of trivalent iron, aluminium, and chro- 40 mium ions in the mother liquor the process is difficult to control particularly as the concentration of these ions tends to build up during the operation of the process I have now found that by the addition to the mother liquor of a substance which has the property of combining the trivalent ion of iron, aluminium and chromium to form complex ions, ammonium sulphate crystals can be obtained with different predetermined length and breadth ratios as desired as in this manner I am able effectively to control the concentration of the trivalent iron, aluminium, or chromium ions in a simple and economical manner.

The following examples illustrate but do not limit the invention.

Example 1 Thirteen solutions of 176 gms. of ammonium sulphate in 300 mls. of water were made up at a temperature above 60 C., and an amount of ferric ammonium alum added until there was 0.05 part of ferric iron present to every 100 parts of ammonium sulphate. The acidity of the solution was adjusted to 3.5 gms. of H2804 per 100 mls. of solution. To each of 12 of these solutions was added a small portion of a substance which forms complex substances with iron. The substances and their weights are given in the table below.

The solutions were agitated overnight in a slowly cooling thermostat, after which the crystals were separated and examined. The following table gives in the first column the substance added, in the second column the weight or" substance added, and in the third column the length to breadth ratio or a description of the crystals formed.

Weight Length to breadth ratio of Substance added added crystals Grams At least 10:1.

1.1 2 1. 4 Crystals resembling sugar cryss. 2. 0 A mixed crop of fine needles and needles of 3%: 1. p 3.0 :1. 3. 0 3:1. 4. 0 A mixed crop of plates and crystuls resembling sugar. 20 3:1. 10 4:1. Cane sugar- 4 5:1. Oxalic acid 1. 0. 5 4:1. Ammonium oxalate--. 0. 25 3:1 With no addition, the solu- Calcium oxalate 0.25 3.5:1 tion gave crystals of 8:1 Sodium oxalate 0.25 3:1 length to breadth ratio.

Example 2 The experiments of Example 1 were repeated using aluminium sulphate in place of ferric ammonium sulphate, there being 0.20 part of A1 to 100 parts of ammonium sulphate. The re- (3) Fe+++ content.0.059 gms/IOO mls. of sults are given in the following table: solution Len tli to Substance Weight 30 o li acid b 5 added added Length to breadth ratio of crystals gms I100 mls gals/100 mls. Crystals produced hrrelatglgh 3. 5 Nil N crystals fi 10 1 3. 0. 05 Fine needles 7:1 2 3.5 0.083 .do 0:1 2 0.1191 .(10.E 1 5:1 :1 some shorter crystals were formed l l crysnn 5 but on repetition of the experiment 83 Fmedgmdles none were formed. 0 Oxalic acid 1 4:1. 0

D0 2 Crystals resembling sugar crystals.

Example 3 The experiments of Example 1 were repeated usin chromium sulphate instead of ferric am- The following two tables show the results of adding oxalic acid and oxalates to a solution containing chromium and aluminum ions.

Chromium.0.025% on salt (added as chromium sulphate) monium sulphate, there being 0.025 part of Cr to 100 parts of ammonium sulphate. The reht Length to sults are given in the following table: Substance added add cd Weiuht Length to Grams Substance added addhcd brcadthratio None". 10-12:1 of crystals Oxallc acid 0.25 3:1 Ammonium oxalate. 0.25 3:1 Sodium oxalate 0125 3:1 Calcium oxalate 0. 25 3:1 At least 10:1. 4 l.

Aluminum.-0.2% on salt (added as aZumz'num sulphate) 2Z1:

' Substance added br c llti l rz l io The above experiments were made with the of c ysta s acidity adjusted to that used in normal saturator practice. Any difierence in acidity or in None Grams the quantity of the iron, aluminium or chromium, -5" will result in a change in the optimum amount Ammonium 1.5 4:1 is of added substance required. This is unpredictable and must be established by experiment in H 1 each case. The following tables show the efiect, 81;? on the crystals formed, of varying the ferric ion 0 1 V 1 0.1g 5:1 content, with the acidity, and with the quantity mmmam of complex-forming substances used, in this case oxalic acid The amount of complex forming compound to be added to the solution so as to obtain am- 1 t m 0 029 gyms/100 l of monium sulphate crystals of any desired length solution to breadth ratio depends upon the concentration of iron, aluminum or chromium cations in the liquor, and upon other factors such as temr zsol Oxalic acid crystalsproduced fi $fi perature and acidity, but may be easily detergmslloo gmS/loo ratio mined for any definite set of conditions by a few simple routine trials. In general, the amount of 3.5 Nil Fine crystals 10:1 compound added may range from 0.1-12 per 8 8$ cent. by weight of the ammonium sulphate pres-- tals. ent, but smaller or larger amounts may be added 0-083 :5 and 211 in certain cases. The amount of free acid in the 7.0 Nil Fine crystals 9:1 solution may be 3.5-7 grins. per 100 mls. of soluit 8: ti tnlltt::::: son, but higher lower amounts 9 acid may 7.0 0. 083 Short rice crystals 2.5:1 be present if desired. For any particular set of conditions, increasing the amounts of the compound or compounds added produces a decrease (2) Fe 00n ent-0-0 4 97/18/100 in the length to breadth ratio of the crystals, solution and it is even possible, by adding sufficiently 5 large amounts of the compound, to produce crys- Length to tals of ammonium sulphate which aresubstan- H2504 oxahcoaclld Crystals produced brea th tlally equidimenslonal. The reduction in length gins/100 gins/10 ratio to breadth ratio of the crystals occurs not only by diminishing the length but also by increasa. 7 8 gg g f gzg mg the breadth whereby the crystals become 3.5 0.083 Short rice and 2:1 more robust 7 0 Nu li g g 10:1 Further complex forming substances which I 005 j have found useful for this invention are: Hydro- 7-0 8 Rice crystals gen iodide, malonic acid, hydrocyanic acids, ni- 75 troso-hydrocyanic acid, thiocyanic acid and their 7 CERTIFICATE OF CORRECTION.

Patent No. 2,178,082. October 1, 19 9.

- JOHN WILFRED RICHARD RAYNER; It 'is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 1 1 for the word "substances" read substance; page 5, first column, line 27, for "complexion" read complex ion; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 5th day of December, A. D. 1959.

Henry, Van Arsdale,

(5 1) Acting Commissioner of Patents. 

